Many car body parts contain cavities that must be sealed to prevent the admission of moisture and contaminating substances, for example, because such substances, particularly moisture, may lead to corrosion of the car body parts. This applies, in particular, to one-piece structures, in which a solid frame is replaced with a unit-body construction that generally contains a multitude of cavities which may accumulate moisture and contaminating substances. These cavities also serve as passages that transmit noise during operation of the vehicle. For example, the generally upright structure of a car body that forms the window opening generally includes an elongated passage or cavity that may collect moisture and contaminating substances and can also transmit undesirable noises. Injecting a sealant into the cavity is generally not satisfactory due to the insufficient sealing and damping provided by known sealing materials, the relatively high costs of such materials, and the irregular seals which known materials provide.
Additionally, the process of injecting foams into car body cavities is generally difficult to control precisely. Typically, an excess of foam must be introduced into the body cavity to adequately prevent the admission of moisture into the cavity while the vehicle is used. Foams also have a limited service life with respect to their flexibility before coagulation, so that the time available for introducing the foam into the cavity of the vehicle is restricted. Alternatives to these foams have been developed, such as other expandable materials which may be introduced into the cavities. Such materials dilate or expand, usually under the influence of heat. A heating process of this type usually takes place during the manufacture of car bodies in an electrocoating oven after the assembly of the bodyshell and the priming of the car body. In such instances, the expandable materials are generally introduced into the cavity together with a carrier material which fixes the expandable material at a certain location in the cavity.
However, known materials that fulfill requirements with respect to stability, durability and corrosion prevention generally do not have a favorable acoustic response in vehicle applications. These materials generally provide insufficient damping of the sound energy that may occur in the cavities during vehicle operation. The users of the vehicles may perceive this as particularly annoying. Noise may be merely sealed off within vehicle cavities by such known materials and expansion-molded parts, i.e., no sound energy is absorbed. Accordingly, there is a need for a material which provides improved sealing and acoustic properties.